1. Field of the Invention
This invention belongs to a technical field of a communication-type navigation apparatus, and more particularly to process of obtaining and updating map data, executed at the time of a route guide and a route search.
2. Description of Related Art
A known navigation apparatus utilizes map data stored in a map data storage medium such as a CD-ROM (Compact Disc-Read Only Memory) or a DVD-ROM (DVD-Read Only Memory). Namely, the navigation apparatus includes a drive unit for the map data storage medium such as a CD-ROM or a DVD-ROM, and reads out map data around the current position of the vehicle according to the movement of the vehicle to display the map data on a LCD (Liquid Crystal Display) or the like attached on the vehicle near a driving seat of the vehicle.
However, in case of using such a storage medium as a data supply source of map data, there is a problem that frequently updating the map data is difficult. The map data is updated in accordance with the expansion of road network. Also, the map data used by the navigation apparatus includes, in addition to road data, information such as neighboring facilities and/or shops (e.g., road-side shops, gas stations and so on). Recently, shops open and shut up relatively frequently. A user who always needs new information should frequently buy and change the map data storage medium, and this is burdensome for the user. In addition, a new edition of map data storage medium is put into the market every certain time period, e.g., every 6 months or every year, and hence the user cannot catch up with the on-going real change of the shops or stores even if he or she buys a new edition every time.
Moreover, recently functions of the navigation apparatus are being improved and sophisticated, and the map data includes more auxiliary data, other than the road data. Hence, the navigation apparatus needs to employ a microprocessor having high-speed processing capability to enable sophisticated route search and/or route guide. This increases the size and the cost of the navigation apparatus.
In order to overcome the above-mentioned problems, recently a communication-type navigation system has been proposed. In such a communication-type navigation system, a navigation apparatus installed on a vehicle and a map data providing center on a communication network communicate with each other by wireless communication, and map data is downloaded from the map data providing center to the navigation apparatus on the vehicle. The navigation apparatus stores the downloaded map data in an internal storage medium such as a hard disk, and performs map display and/or route guide by using the stored map data. Examples of such a communication-type navigation apparatus are disclosed in Japanese Patent Applications Laid-Open under No. 7-262495 and No. 10-96644.
In such a communication-type navigation system, by updating the map database on the map data providing center side, a user can always obtain and use newest map data by communication with the map data providing center.
A route search is known as a useful function of a navigation apparatus. The route search is a function that calculates and displays a travel route to a destination designated by the user, and the calculation of the travel route is basically executed based on the map data. In order to guide the user to drive along the travel route obtained by the route search, the navigation apparatus needs to have map data covering the travel route.
However, in a communication-type navigation apparatus, the map data is basically obtained by the communication with the map data providing center. Therefore, if all necessary map data covering the travel route to a far destination is downloaded from the map data providing center by communication, considerable communication cost is required. Therefore, it is desired that the user can obtain only necessary map data or road data dependently upon various situation.
In addition, the map data is periodically updated, and it is preferred to obtain and use as new map data as possible to effectively utilize the functions of the navigation apparatus such as the route search function. Hence, ideally it is preferred to obtain newest version for all map data covering the travel route determined by the route search. However, in consideration of communication cost, it is required to efficiently update only necessary map data.